The development of the human lung as reflected by the surfactant phospholipids in amniotic fluid continues to be studied. This now has resulted in the Lung Profile (the L/S ratio, plus percentages of disaturated lecithin, phosphatidyl inositol and phosphatidyl glycerol) which permits exact diagnoses of maturity of the lungs of infants of diabetic mothers as well as of those lungs of infanct with low L/S ratios which may be mature from the presence of phosphatidyl glycerol although the L/S ratio may be less than 2.0. Thus this test produces accuracy of predictions of lung maturity to as close to 100 percent as a biological test can be. Additionally, studies are in progress in rabbits of the regulation of surfactant lipid biosynthesis.